Enzymes, intermediates and cofactors of the energy yielding pathways will be measured in the cochlear epithelia and the influence on these parameters of ischemia, ototoxic drugs and degeneration of the olivo-cochlear nerve fibers will be examined in the structures supposed affected by such measures. The metabolic rate of selected structures of the cochlear will be estimated and alterations of the energy use rate induced by experimental conditions will be studied. Enzymes of acetylcholine and gamma-aminobutyric acid (GABA) metabolism will be measured in sensory receptors and the spiral ganglion. GABA and glutamate levels will be determined under various experimental conditions. Radioactive glucose, amino acids and purines will be injected into the perilymph and the incorporation into proteins and nucleic acids of the organ of Corti will be determined. If the design of these latter methods is successful the influence of ototoxic antibiotics on protein and nucleic acid biosynthesis in the organ of Corti will be examined. As time allows attempts will be made to extend these studies to the cellular level, to investigate pure populations of hair cells, Deiter cells, Hensen cells and ganglion cells. It appears justified to expect from the pursuit of such studies valuable information about the peculiarities of the bioenergetics, the role of transmitters, and of protein and nucleic acid metabolism in the physiology and pathology of cochlear structures.